Rotary hydraulic motor



June 5, 1962 G. M. BARRETT 3,037,488

ROTARY HYDRAULIC MOTOR Filed Jan. 8, 1960 I 3 Sheets-sheaf 1 INVENTOR.aeowefl f. BarreZZ BY J9 7774-441 DA 4 G. M. BARRETT ROTARY HYDRAULICMOTOR June 5, 1962 3 Sheets-Sheet 2 Filed Jan. 8, 1960 INVENTOR. 6 60796Ba rreiz" June 5, 1962 c. M. BARRETT ROTARY HYDRAULIC MOTOR 3Sheets-Sheet 3 Filed Jan. 8, 1960 B n m I 2 M M m m fi w I .EzaJOB R O mM Gsotzee M. BARRETT it PM 27% z W ATTORNEYS UnitedStates Patent3,037,488 ROTARY HYDRAULIC MOTOR George M. Barrett, Galt, Ontario,Canada Filed Jan. 8, 1960, Ser. No. 1,381 7 Claims. (Cl. 121-61) Thisinvention relates in general to new and useful improvements in hydraulicmotors, and more particularly relates to a new and useful rotaryhydraulic motor.

The present invention relates to rotary hydraulic motors of the typewherein the cylinders of the hydraulic motor are mounted in a rotor inradiating relation and the pistons of the individual cylinders reactagainst a cam track to urge the rotation of the rotor. Heretofore, theobtaining of a pressure contact between the piston and the cam track hasbeen a problem, in that it is necessary to provide for a rolling contactbetween a piston part and the cam track. As the result, numerous typesof complicated roller assemblies have been provided. These, of course,are both expensive and subject to failure. The present invention isbelieved to distinguish over the prior rotary hydraulic motors. byproviding pistons which are rotatable within their individual cylindersand which have rolling contact with the cam tracks so that one-piecepis-- tons may be utilized as opposed to the normal three or more piecepistons now in use.

Another object of the invention is to provide a rotary hydraulic motorwherein the lengths of the cylinders of the rotor of the motor are atleast as great as the lengths of the pistons so that the pistons may becompletely retracted within the cylinders, thus permitting the rotor tofreely rotate within the housing of the motor without any circulation ofhydraulic fluid whatsoever.

Still another object of the invention is to provide a novel hydraulicmotor of the rotary type wherein the cam track is of a shape whichprovides for linear fluid consumption, and therefore eliminates pulsingand variations in torque regardless of the number of pistons carried bythe rotor.

A further object of the invention is to provide a novel hydraulic motorwhich is provided with a fixed stator and port assembly, and a fixedcamtrack, together with a rotor which rotates about the stator andwithin the cam track, the rotor being provided with any desired numberof cylinders and pistons without changing the other structure of themotor.

Still another object of the invention is to provide in a rotaryhydraulic motor a port arrangement of a nature wherein when the portsare opened and closed, there is approximately zero fluid flow, and theport opening is proportional to the piston speed, whereby flow velocityof the fluid at the port is substantially uniform.

A still further object of the invention is to provide a rotary hydraulicmotor wherein the working fluid is applied in such a way that most ofthe load on the working parts of the hydraulic motor is balanced out,and fluid pressure is not applied to the structural parts of the motor.

With the above, and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims, and theseveral views illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is an elevational view of a fluid motor constructed inaccordance with the invention and coupled to a hydraulic system foroperation, the hydraulic system being only schematically illustrated.

FIGURE 2 is an enlarged end view of the fluid motor of FIGURE 1, andshows the connections of the hydraulic lines thereto.

FIGURE 3 is an enlarged longitudinal vertical sec- 3,037,488 PatentedJune 5, 1962 tional view taken along the section line 3-3 of FIGURE 2and shows the internal construction of the fluid motor.

FIGURE 4 a transverse sectional view, taken along the section line 4-4of FIGURE 3, and shows the arrangement of the cylinders of the rotor,the ports in the stator, and the shape of the cam track.

FIGURE 5 is a transverse sectional view taken along the section line 55of FIGURE 3, and shows the details of the stator in the vicinity of oneend thereof to illustrate the connection between the return flow portsthereof.

FIGURE 6 is a transverse sectional view taken along the section line 6-6of FIGURE 3, and shows the arrangement of the inlet ports in the statorand the manner in which they are connected together.

FIGURES 7, 7A, and 7B are schematic views illustrating the relationshipof the various components of the hydraulic motor for one cylinder andpiston when the piston is in its fully retracted position and show therelationship of the spacing between the cam track surface and the rotorand the relationship of the cylinder and an associated port.

FIGURES 8, 8A, 8B, 9, 9A, 9B, 10, 10A and 10B are views similar toFIGURES 7, 7A and 7B, respectively, and show the piston and cylinder insequentially rotated positions from that of FIGURE 7.

Referring now to the drawings in detail, it will be seen that theembodiment of the invention illustrated in FIG- URES 1 through 6,inclusive, is generally referred to by the numeral 10. The hydraulicmotor 10 includes a twopiece housing, generally referred to by thenumeral 11. The housing 11 includes a generally cylindrical body member12 and an end plate 13. The end plate 13 is suitably secured to the body12 in sealed relation by means of a plurality of recessed cap screws 14.The cap screws 14 are best illustrated in FIGURES 2 and 3.

The end plate 13 carries a centrally located stator 15 which isillustrated as being formed integrally with the end plate 13, but whichmay be separate therefrom. The stator 15 is illustrated as having acentral bore 16 therethrough which, if desired, may be omitted, or whichmay be used to receive a drive shaft connected to the rotor, if sodesired.

The stator 15 has a generally cylindrical outer surface and acylindrical rotor 17 is received thereover. In the simplest form of theinvention, as illustrated in the drawings, the rotor 17 is journaled onthe stator 15. The rotor 17 is provided with a plurality of cylinders18, the cylinders 18 having their axes extending radially from thecenter of the rotor 17, and the cylinders opening through oppositesurfaces of the rotor 17. A piston'19 is disposed in each of thecylinders 18. It is to be noted that in this form, of the invention,each piston 19 is in the form of a ball. The diameter of the individualpiston 19 is substantially equal to the diameter of its respectivecylinder 18. Furthermore, the length of each cylinder 18, that is, thethickness of the rotor 17, is equal to or slightly greater than thediameter of each piston 19. However, it is to be understood that each ofthe pistons 19 may be totally recessed within its respective cylinder 18so that no portion thereof will project outwardly be-' yond the confinesof the rotor 17. r

The housing body 12 has an interior surface; defining a cam track 20.The cam track 20 is illustrated as having three lobes, although thenumber of lobes may vary as is desired. Each of the lobes of the camtrack 20 has a pair of similar thrust surfaces 21, 22, the pistons 19reacting against one of the thrust surfaces to effect the rotation ofthe rotor and the other of the thrust surfaces reacting against thepistons to return the pistons to their retracted positions as the rotor17 rotates. The direction of rotation of the rotor 17 will control whichof the thrust surfaces is reacted against by the pistons and whichreacts against the pistons to return them to their positions within therotor 17. The thrust surfaces can be interchangeable in function topermit reversal of rotation.

The outer surface of the stator 15 in alignment with the cylinders 18 asthey rotate about the stator 15, is provided with a plurality of ports.These ports include fluid pressure ports 23 and fluid return ports 24,the ports 23 and 24 being alternated about the circumference of thestator 15. A first longitudinal bore 25 extends partially through thestator 15 and opens through the end wall 13. The bore 25 opens into oneof the ports 23 and is communicated with the others of the ports 23 by agroove 26 which extends about the circumference of the stator 15 andintersects all of the ports 23. The rotor '17 closely engaging the fixedstator 15 prevents leakage out of the recess 26 for all practicalpurposes.

The outer portion of the bore 25 is internally threaded, as at 27, and afitting 28 is threaded thereinto. The fitting 28 is part of a hydraulicfluid supply line 29.

A second bore 30 extends into the stator 15 through the end wall 13 inofrset relation to the center of the stator 15. The bore 30 intersectsone of the ports 24 and opens thereinto. A recess 31 is formed in theexterior surface of the stator 15 remote from the end wall 13 andintersects all of the ports 24. Thus, hydraulic fluid may be returnedthrough the ports 24, through the recess 31 and into the bore 30. Atthis time, it is pointed out that the ports 24 extend beyond the ports23 away from the end wall :13, and the ports 23 extend beyond the ports24 towards the end wall 13, whereby the recess 26 does not intersect anyof the ports 24 and the recess 31 does not intersect any of the ports23.

The outer portion of the bore 30 is internally threaded, as at 32, and afitting 33 is threadedly engaged therein. The fitting 33 is part of thehydraulic fluid return line 34.

In the form of the invention illustrated, the rotor has a reducedcylindrical extension 35 which projects beyond the housing 11 and whichhas suitably coupled thereto a drive shaft 36. The rotor extension 35 issealed with respect to the stator 15 by means of a suitable sealing ring37 and with respect to the housing body 12 by means of a suitablesealing ring 38. If desired, the sealing rings 37 and 38 may be in theform of scaled bearings. This, of course, is merely a question ofmechanical design.

There will, of course, be a small amount of leakage past the pistonsinto the space between the rotor 17 and the cam track 20. In order thatthe hydraulic fluid may be returned therefrom and thus not prevent theproper operation of the hydraulic motor 10, a drain bore 39 extendsthrough the end wall 13 at the bottom of the housing 11. The bore 39includes an outer enlarged portion 40 which is internally threaded andwhich receives a fitting 41 (FIGURE 1) of a drain line 42.

Referring now to FIGURE 1 in particular, it will be seen that thehydraulic system for the hydraulic motor 10 is schematically illustratedas including a reservoir 43 having disposed therein a hydraulic fluidsupply. A line 44 extends from the reservoir 43 to a pump 45. Thehydraulic fluid supply line 29 is connected to the outlet of the pump45. The hydraulic fluid return line 34 and the drain line 42 areconnected to the reservoir 43 for re turning hydraulic fluid thereto.

As is best illustrated in FIGURE 4, it will be seen that the ports 23are so arranged that when the rotor 17 rotates and one of the cylinders18 approaches a lobe of the cam track 20, the cylinder will uncover theport 23 and hydraulic fluid will be admitted to the cylinder behind itsrespective piston 19. The piston 19 will be urged outwardly and willengage one of the thrust surfaces 21, 22 which, for purposes ofdescription, may be considered the thrust surface 21. The reaction ofthe piston 19 on the thrust surface 21 will result in a force urging therotation of the rotor 17 about the stator 15. This rotative force willcontinue until such time as the piston 19 reaches the midpoint of theparticular lobe, at which time, the respective port 23 will bemomentarily closed by the rotor 17, and the particular cylinder 18 willhave completely moved away from the port 23. Immediately thereafter, thecylinder 18 will uncover the next adjacent port 24, and as the piston 19engages the thrust surface 22, the reaction of the thrust surface 22 onthe piston 19 will urge the particular piston 19 inwardly with thepiston 19 forcing the hydraulic fluid within its respective cylinder 18inwardly and out through the return port 24. Since there is very littleback pressure in the return system of the hydraulic motor 10, it will beseen that there will be very little resistance to the inward movement ofthe piston 19 and therefore very little loss of efficiency.

The number of lobes on the cam track 20 has been illustrated as three,and the number of cylinders and pistons has been illustrated as eight.Thus, each time the rotor 17 makes a complete revolution, there will be24 power strokes. This provides for a relatively smooth forceapplication.

The cam track 20 is symmetrical about the center line of the rotor, andis in the form of a modified polytrochoidal curve which permits the useof pistons of any number and of a variety of shapes. It will be readilyapparent that the pistons 19, being of a ball configuration, rollagainst the cam track 20 and thus greatly reduce fric tion losses.

It will be seen that when a piston 19 has reached the end of its radialtravel, the respective ports are then opened or closed, and the portsare opened and closed at a maximum speed. As a result of this, the flowof fluid through any port is virtually nil when it is being opened orclosed. Consequently, cavitation, surging eddying and hydraulic shockare reduced to a very small amount and are almost independent of speed.The sum of the radial speed of all the pistons at any given time isequal to a constant. This results in a linear constant fluid flowthrough the motor.

Reference is now made to FIGURES 7, 7A, 7B through 10, 10A and 10Bwherein it is clearly indicated that the rate of divergence of the camtrack surface 21, for example, from the rotor 17 is the same as the rateof opening of the associated port 23, for example, such that thevelocity of fluid flow through the port at a given speed of operation ofhydraulic motor 10 remains constant. In accordance with the invention,in order to eliminate for all practical purposes any turbulence in flow,it is desired that the velocity of fluid flow through any port remainsconstant, and since the cross section of the cylinders 18 remainsconstant, only the movement of the piston 19 relative to the rotor 17and the cross section of the opening of the port can vary. Therefore, itfollows that in order to provide for the desired operation of thehydraulic motor 10, the rate of piston movement must be the same as therate of port area increase, and since the rate of piston movement iscontrolled by the divergence of the cam thrust surface from the rotor,the rate of divergence of the cam thrust surface from the rotor must bethe same as the rate of port area increases.

In FIGURES 7A, 8A, 9A and 10A, a comparison of the spacing between theouter surface of the rotor 17 and the cam surface 21, for example, isshown. In FIGURE 7A the rotor is touching the respective cam surface 21so that the dimension A is zero. It will be seen that in FIGURES 8A, 9Aand 10A the dimension A rapidly increases for a corresponding rotationalmovement of the rotor. In a like manner, in FIGURE 7B the cylinder 18does not uncover any portion of the port 23. On the other hand, if therotor rotates, the cylinder 18 progressively uncovers the port 23 anddue to the fact that the cylinder in the particular form of hydraulicmotor illustrated is circular, there is a rapid rate of change in theuncovered area of the port as compared to the relative circumferentialmovement of the cylinder with respect to the port. It will be readilyapparent upon comparing FIGURES 7A and 7B through 10A and 10B that therate of divergence of the cam surface 2.3 from the rotor 17 is the sameas the rate of increase in cross section of the port open area.

It will be observed that the hydraulic fluid is applied into theinterior of the hydraulic motor 10 in such a way that most of the loadon the working parts of the hydraulic motor is balanced out and thefluid pressure is not applied to the structural parts of the hydraulicmotor. It is also to be noted that the number of lobes on the cam trackand the number of pistons is arbitrary as the hydraulic motor willoperate with almost an unlimited number of combinations, provided thatthe number of pistons is not equal to the number of lobes.

The spacing of the ports is arranged in such a manner that the force onthe pistons is translated into a turning force on the rotor. As eachpiston reaches its maximum radial travel, the outlet port is closed andthe return port is opened. Further travel results in the piston beingpushed inwardly, forcing the working fluid through the return port andreturning the piston to its inner position ready for another pressurestroke. It will be seen that mechanical clearance or backlash isvirtually eliminated by this construction. By reason of negligiblebacklash, reversing of the motor can be almost instantaneous withoutmechanical shock or overrun.

It will be seen that by placing the pistons in different planes ofrotation, a very large number of cylinders can be employed withoutintroducing mechanical complication thereby permitting a very muchincreased torque output at lower speeds. The upper limit of the speed ofthe motor is limited only by the volume of hydraulic fluid which can beadmitted by the inlet and return passages. It will also be seen that themotor can be mounted with the so-called rotor in a fixed position androtary motion being delivered through the rotation of the outer case orhousing about the rotor. In addition, reversing can be accomplished bychanging the direction of fluid flow, or by altering the phaserelationship between the stator ports and the cam track.

At this time, it is also pointed out that changing the phase relation ofthe ports and cam track will result in altering torque and speedcharacteristics of the motor, and will make possible its efficient usewith compressible fluid such as steam and air.

Although the motor may be operated in a manner to eliminate the brakingaction thereof, if a pressure difierential is maintained across theinlet and return passages, a braking effect on a rotating member drivenby the motor can be accomplished.

From the foregoing, it will be seen that novel and advantageousprovision has been made for carrying out the desired end. However,attention is directed to the fact that variations may be made in theexample apparatus disclosed herein without departing from the spirit andscope of the invention, as defined in the appended claims.

I claim:

1. A rotary hydraulic motor comprising a housing, a centrally locatedstator supported by said housing, an inner wall of said housing defininga cam track, a cylindrical rotor mounted on said stator for freerotation, said cam track having a plurality of circumferential thrustsurfaces, said rotor having a plurality of cylinders, a piston freelypositioned within each of said cylinders for reciprocatory movement,inlet and outlet hydraulic passages in said stator and alternatinglyopening through the surface of said stator in the form of ports disposedin operative relation to said thrust surfaces, said cylindersalternatingly uncovering said inlet and outlet ports as said rotorrotates with the hydraulic fluid passing through said inlet portsforcing said pistons into direct engagement with said cam track, saidthrust surfaces each diverging from said rotor at the same rate as theport area increases into said cylinders whereby fluid flow velocity issubstantially constant.

2. The rotary hydraulic motor of claim 1 wherein said cam track isgenerally of a polytrochoidal curve shape.

3. The rotary hydraulic motor of claim 1 wherein said cam track isgenerally of a polytrochoidal curve shape, and said cylinders are eachof a circular cross section.

4. The rotary hydraulic motor of claim 1 wherein the lengths of saidcylinders are at least as great as the lengths of said pistons wherebysaid pistons may completely retract within said rotor and said rotor mayrotate without fluid flow.

5. The rotary hydraulic motor of claim 1 wherein said cam track isgenerally of a polytrochoidal curve shape, said cylinders are each of acircular cross section, and said pistons are in the form of balls havingrolling con tact with said cam track.

6. The rotary hydraulic motor of claim 1 wherein said cam track and saidstator are carried by separate parts of said housing and are releaseablyconnected together.

7. The rotary hydraulic motor of claim 1 wherein the relationship ofsaid ports, said cam track and said cylinders is so related wherein eachpiston is at an end of its travel at the time the cylinder thereof movesto uncover and close said ports.

References Cited in the file of this patent UNITED STATES PATENTS388,379 Strait Aug. 21, 1888 459,735 Benham Sept. 22, 1891 2,101,829Benedek Dec. 7, 1937 2,823,619 May Feb. 18, 1958 2,882,831 Dannevig Apr.21, 1959 FOREIGN PATENTS 275,796 Germany July 1, 1914

